Apparatus for locating water-bearing strata in bore holes of flowing wells



Sept. 29, 1925.

F. W. HUBER APPARATUS FOR LOCATING WATER BEARING STRATA IN BORE HOLES 0FFLOWING WELLS Filed Sept. 2, 1924 [N VEN TOR. FreaPr/Z'K H4 Haber ATTORNE Y.

Patented Sept. 29, 1925.

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APPARATUS FOR LOGATING WATER-BEARING STBATA. IN BORE HOLES OF FLOWING Toall whom it may camera:

Be it known that I, FREDERICK W. HUBER,-

a citizen of the United States, residin at Riverside, in the county ofRiverside, tate of California, have invented a new and useful Apparatusfor Locatin Water-Bearm Strata in Bore Holes of F owing Wells, 0 whichthe following is a specification.

This invention relates to a method for 10- eating water bearing stratain bore holes n oil or gas bearing formations and the mam object of theinvention is to provide a means and method whereby the location of suchwater bearing strata may be positively determined without interruptingthe operation of the well.

In the operation of 011 wells it often occurs that after the oil hasbeen flowing for some time either under natural pressure or with theassistance of pumping, there is a tendency for water (so-called ed ewater) to enter the well from water bearing strata adjac ent to the borehole, this tendency increasing as the gas pressure in the welldiminishes and often result-ing eventually in the abandonment of thewell. In some cases, also, it is not possibile to start production ofoil, because of flow of water into the well.

My invention provides for determining the location of water bearingstrata while the well is in operation or before it starts into operationso that steps can be taken promptly to cement out such strata so as toexclude water from entering the Well. from such strata and to start ormaintain the well in productive operation.

My invention provides for introduction within the bore hole of a flowingwell a means for producing at any one of the desired levels in the wella zone of fresh water or water of relatively different salinity andfurther introducing into the well a means for measuring the salinity ofthe liquid adjacent to such fresh water zone in such manner that anyvariation of such salinity due to proximity-of the strata bearing saltwater will result in a corresponding variation in electrical measurementthereby determining the location of the water bearing stratum. Thesalinity of the liquid is referably measured by introducing electro emeans, connected to a source of (preferably alternating) current ofsubstantially uniform Application filed September 2, 1924. Serial No.735,330.

voltage into the well in such manner that such electrode means areexposed to the liquid inthe well and measurin the resist ance of theliquid so exposed to t e electrode means in any suitable manner.

The accompanying drawings illustrate the manner in which my inventionmay be carried out and referring thereto:

Fig. 1 1s a diagrammatic vertical section of-a well with the measuringappliances in place therein.

Fig. 2 is a section of the exploration tube and a side elevation of theresistance meas uring appliance with the electrical circuits thereforshown diagrammatically.

Flg. 3 is a Vertical section of the electrodes.

Referring to Fig. 1 a well casing is shown at 1, said casing beingassumed to constitute the oil string which extends down .into the 011sands and which is perforated in the usual manner as indicated at 2 forinflow of oil. 3 indicates the water string which is assumed to becemented in the usual manner so as to shut off all water strata abovethe oil sands, and casing 1 is further provided at its upper end withthe usual means for carrying off the oil for example through delivv erypipe 4.

The measuring means used according to my.1nvent1on comprises a conductorcable 5 or self supporting cable means which is providedwith electrodes6 and7 at its lower end and is flexibly connected at its upper end to asuitable measuring circuit as hereinafter described. This conductorcable 5 carrying the electrode, is mounted within a vertical explorationtube 8 which is formed as a string of suitable tube sections in theusual manner in the art so as to enable it to reach from the top of thewell down to the level of the oil sands. This tube may be supported byan suitable elevator means such as indicate at 10 so as to be raised andlowered at will and if necessary is passed through a stufling box 13 inthe casing head 14 in such manner that the lower endof the tube membermay be raised and lowered throughout the height represented by theperforated portion of the oil string. The cable 5 is also mounted forvertical movement within the pipe 8, for example by means of a sleeve 16mounted 45. transformer whose primary winding 15 is .water of low salineconcentration.

on said cable and sliding through a stufiing box 17 on the head 18 atthe upper end of said pipe 8. Said head 18 may e provided with aflexible pipe connection 20 leading to a source of supply of fresh wateror Electrodes indicated at 6 and? may be mounted in any suitable mannerfor example within a cylinder 9 which may be of insulat ng material, theelectrodes in any case belng insulated from one another and beingmounted a definite distance apart and the cylinder being open andpreferably being open at both ends so as to allow free access of liquidto said electrodes. The said electrodes 6 and 7 are connectedrespectively to wires or conductors 22 and 23 within the said cable 5.The conductors 22 and 23 are preferably formed as steel wires or cables,

for the sake of strength and in that case are self-supporting, beingeither embedded in insulation to form a single conductor cable or beingseparately insulated and extending side by side to form two conductorcables.

Any suitable circuit means may be provided for applying the electriccurrent or potential to the wires leading to the electrodes so as tomeasure the resistance of the medium presented between the electrodes,for example, as shown in Fig. 2, said electric measuring means maycomprise a Wheatstone bridge 21 of usual construction, which isconnected to a source of current or electric potential described belowand to the circuit wires 22 and 23. It is essential to the presentinvention that alternating current should be used in measuring theelectrical resistance so as to avoid errors which would result frompolarization in case direct current were used, and it is also importantthat no ground connections should be present, and in order to satisfythese requirements I prefer to use as a source of current a connected toany suitable alternating current supply circuit, either single phase orpolyphase, and whose secondary winding 24 is connected by wires 25 and26 to opposite terminals of the Wheatstone bridge 21. The intermediateterminals of the Wheatstone bridge are connected in, the usual manner toa null point indicator 27 which is of a type adapted for operation byalternating current. Said null point indicator may be provided withenergizing circuit connections 28 and 29, including resistance or lamp30, for the field magnet coil thereof, so as to apply say 110 volts tosuch coil, to produce a magnetic field which operates upon an armaturecoil connected by circuit wires 31 and 32 to the intermediate terminalsof the Wheatstone bridge in the usual manner of such alternating currentmeasuring means. Any other electrical measuring means, responsive toalternating current may, however, be used. The transformer used may beof the iron core type, transforming for example from 110 to 6 volts, thelatter voltage bein applied to the wires leading to the electro e means.By maintaining only about 6 volts in the lines leading to the electrodesI ensure operation of the system even when the cable insulation hasbecome damaged by oil or otherwise as long as there-is no actual shortcircuit.

In order that the electrode means shall operate effectively under theconditions existing in the column of liquid in the test operation ashereinafter set forth it is necessary that the surface of the electrodeswhich are in contact with the liquid not be wetted by oil but only bywater and saline solutions. For this purpose I have found it desirableto coat the surface of the metal body or conductors forming theelectrodes with a gelatinous substance and I have found that eithergelatinous silica or agar may be used advantageously for this purpose.The gelatinous silica is however only applicable to latinum or goldelectrodes or to their aci resisting alloys. To coat such an electrode Iallow water glass of about 1.15 sp. gr. to harden in a thin film uponthe electrode and then immerse it in a-very dilute solution of mineralacid, which in the course of a few hours will form a gelatinous coatingof silicic acid. This is then washed free of electrolytes and kept in awater saturated atmosphere until ready for use.

lVith the baser metals such as nickel which I prefer to use in actualfield work) I simply coat the cleaned electrode surface with a thin filmof agar dissolved (dispersed) in hot distilled water, by dipping theelectrode in the agar infusion and allowing to set, repeating thedipping and setting until a uniform and thin film is obtained over theentire electrode surface. The elec trode after the agar has set (forminga stiffjelly-like mass), is kept in water until wanted for use. It isalso of advantage to first cover the cleaned electrode with a finecambric cloth and then saturate this cloth with hot agar infusing andbuilding up on this covering a fine glaze of set agar. It is also ofadvantage, for particularly severe usage, to harden the agar by ahardening agent such as formaldehyde or alum. But this is generally notnecessary.

The operation of the invention is as follows:

Assuming that a flowing oil well has been in producing operation andthat the presence of water with the oil produced indicates intrusion ofwater into the well, the location of the water bearing stratum or stratais determined by inserting the measuring device above described into theoil well and operating it in the following manner. The

exploration tube 8 havin been brought to osition, for example wit itslower end adacent the bottom of the oil strin fresh water is forced downthrough sai pipe so that said pipe and the lower portion of the liquidcolumn in the well as far as possible.

I also prefer to maintain a hydrostatic pressure inthe water su ply pipe8 sufficient to just balance the fluid pressure in the well, so as toprovide substantially a static column of li uid in the well and permitthe diffusion of sa t from surrounding water sands to take place evenwhile no water is flowing from the sand. If at this time there ispresent a water bearing stratum adjacent the perforated portion of theoil string and adjacent this fresh water column there will be diffusionof salt from such water stratum into the body of fresh water in saidcolumn directly opposite such water stratum, resulting in a zone ofrelatively high saline concentration adjacent the stratum bearing saltwater. The said water column may then be explored by lowering the pipe 8to different positions so that the lower end of said-pipe is presented,at different levels in said column and after each of said loweringoperations the measurement of saline concentration at or adjacent to thelower end of the pipe is made by means of the electrical devices abovedescribed, the cable 5 being assumed to be in position to cause theelectrodes 6 and 7 to be exposed tothe liquid directly below the lowerend of the pipe 8, and the resistance of the liquid between saidelectrodes being then measured b operation of the Wheatstone bridge inwe] known manner or by any other suitable de-. vice for measuringelectrical resistance. While the pipe 8 is being brought to position oris being lowered to the bottom of the well the carrier member 9 for theelectrodes 6 and 7 may be withdrawn within said pipe (by raising sleeve16 and cable 5) soas to be protected and said carrier member may belowered below the lower end of the pipe only when measurement is to bemade. In some cases I prefer to momentarily relieve the hydrostaticpressure on the water supply tu e 8 just prior to or simultaneously witeach conductivity measurement so as to cause the liquid in the welladjacent the lower portion of such tube to be forced upwardly within thesame 'a short distance and ensure that the electrodes are surrounded bysuch liquid "diffusion of salt into the zone a rather than by freshwater from the water supply tube. B making a series of measurements atdi erent levels throughout the range of vertical hei hts represented bythe per orated portion 0 the oil string, and plotting the resistancemeasurements so obtained at various de ths the depth of any stratumthrough whic sa t water is penetrating the well will be indicated by acorres lplondmg low point in the resistance curve. e position of thewater bearing stratum or strata having been determined in this mannerthe proper steps can be taken to'seal or cement off such water bearingstratum from-the well so as to enable the well to continue in operationin the production of oil.

Alternatively to the above described method of operation my inventionmay be carried out as follows: The pipe 8 having been lowered to nearthe bottom of the oil strin suflicient fresh water is assed throng saidpipe to displace the oiFand salt water from only the lower portion ofthe oil string adjacent the lower end of ipe 8, and a resistance readingis then ta en as above ,described, the electrodes 6 and 7 being loweredslightly below the pipe 8 for that purpose, andthe column of liquidbeing preferabl preserved in a static condition during sue measurement,by shutting off the flow of oil from the well and balancing the pressureby the hydrostatic head in the water supply ipe as above described. Insome cases the ydrostatic pressure in the tube 8v may be momentarilyrelieved at the time of making a conductivity measurement, for thepurpose above described. The pi 8 is then ralsed a suitable distance andanother reading taken and this operation of successive elevation of thepipe and resistance reading being continued until the lower end of thepipe 8 reaches the upper limit ofthe perforated portion of theoilstring. In this case, as before, the presence of any water bearingstratum will be indicated by an increase in conductivity or decrease inresistance of the liquid opposite such stratum by reason of jacent suchstratum. This method of operation last described however has theadvantage that the.

measurement is made immediately after the introduction of fresh water atthe measured part of the liquid columin so that more uniform as well asmore accurate results are obtained in some cases. In some cases, when.

the water entering the borefi 'hole from the water stratum hasrelativelylow salinity, it will be desirable to introduce into the well(instead of fresh water) water of relatively high salinity, thereadingfor a zone opposite such a water stratum thus indicatm relatively highresistance, and in gener my invention provides for establishing in thebore hole a ,water column of different saline concentration from that ofthe water in the water bearing stratum to located, and then determiningthe location in such a water column of any zone difl'ering in salmityfrom the normal salinity of such water column.-

The novel electrode described herein is claimed in a copending case756,156, filed December 15,1924.

What I claim is:

1. In combination with an oil well a ipe independent of the oil wellcasin exten ing into said well and provided wit means for passing watertherethrough into the well, means for raising and lowering said ipeinsulated conductor means exten ing through said ipe and provided withelectrodes adapted to be ex osed to the liquid in the well, andelectrica circuit means connected to said conductor means and providedwith means for measurin the resistance of the liquid between said eectrodes.

2. An apparatus as set forth in claim 1 in i which said insulatedconductor means is movably mounted in a vertically movable pipe throughwhich it extends to permit of the electrode means being withdrawn withinor projected below said pipe.

3. An a phance for measuring the resistivity of the liquid at difi'erentlevels in a well,,comprisin' a vertically movable pipe, independent of te well casm such movable pipe bein provided wit means for forcing waterherethrou h, insulated conductor means extending t gh said pi andprovided with electrodes adapted to b: exposed to the liquid in thewell, and electrical circuit means connected to said conductor means andprovided with means for measurin the resistance of the liquid betweensai electrodes.

4. A. combination as set forth in claim 3 in which said insulatedconductor means is movably mounted in the pipe throu h which it extends,to permit of the electr e means being withdrawn within or projectedbelow said pipe.

In testimony whereof I have hereunto subscribed my name this 21st day ofAugust FREDERICK W. HUBER.

